The present invention relates to a process for the determination of the aging condition of an exhaust-gas catalyst for an internal combustion engine which is fitted with .lambda.-controlled regulation of the fuel/air ratio.
The fulfillment of certain legal requirements for exhaust-gas composition can only be achieved by catalytic treatment of the exhaust gases. In order to ensure that the catalyst works optimally during normal driving operation, the fuel/air ratio must fluctuate between very tight limits about the stoichiometric ratio. This is accomplished by connecting a .lambda.-probe system in front of the catalyst, the system being used to determine the residual oxygen in the exhaust gas.
Conclusions on the fuel/air ratio are drawn from the voltage (EMF) produced by the .lambda.-probe via a probe line. The desired .lambda.-control point is set via adjustable electronic parameters, such as threshold value, operating point, integrator characteristics and retardation times. On the basis of the characteristic curve of the probe, the regulator connected to the probe generally works as a two-position controller, such that the proportion of fuel in the fuel/air mixture is increased or decreased when the voltage produced deviates from the operating point. Due to the gas transit times in the engine, a constant oscillation between a rich and a lean fuel/air mixture is thereby produced.
It is known that the catalysts react relatively sensitively to overheating and, in particular, to impurities and additives, lead compounds for example, in the fuel. In addition, a certain amount of aging of the catalysts occurs under the hard operating conditions in a vehicle. All the factors mentioned above lead to a reduction in performance of the catalyst.
As soon as the reduction in performance of the catalyst has reached a certain level, the catalyst should be replaced. If at all possible, this should be done before the catalyst is so badly destroyed that its non-operative condition can even be observed externally. Thus, a simple process for testing the aging condition of a catalyst in a combustion engine is desirable.
One of the objects of the present invention is to provide a simple process which can be carried out in practically any motor vehicle workshop to determine the aging condition of the catalyst.
These and other objects are achieved in a process for measuring the aging condition of a catalyst for an internal combustion engine that has .lambda.-controlled regulation of the fuel/air ratio that is switched from rich to lean and lean to rich, by providing the delaying of the switching of the fuel/air ratio, and measuring the amount of combustible components in the exhaust gas after it has passed the catalyst.
Further objects, features and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings, which show for purpose of illustration only, an embodiment constructed in accordance with the present invention.